// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Seccomp BPF helper functions, modified from the Chromium OS version. The
// original notice is below.
//
// Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
// Author: Will Drewry <wad@chromium.org>
//
// The code may be used by anyone for any purpose,
// and can serve as a starting point for developing
// applications using prctl(PR_ATTACH_SECCOMP_FILTER).

#include "sandboxed_api/sandbox2/util/bpf_helper.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int bpf_resolve_jumps(struct bpf_labels *labels, struct sock_filter *filter,
                      size_t count) {
  if (count < 1 || count > BPF_MAXINSNS) {
    return -1;
  }
  if (labels->count > BPF_LABELS_MAX) {
    return -1;
  }
  /*
   * Walk it once, backwards, to build the label table and do fixups.
   * Since backward jumps are disallowed by BPF, this is easy.
   */
  for (size_t i = 0; i < count; ++i) {
    size_t offset = count - i - 1;
    struct sock_filter *instr = &filter[offset];
    if (instr->code != (BPF_JMP + BPF_JA)) {
      continue;
    }
    if (instr->k >= labels->count) {
      fprintf(stderr, "Label index out of bounds: '%d'\n", instr->k);
      return 1;
    }
    switch ((instr->jt << 8) | instr->jf) {
      case (JUMP_JT << 8) | JUMP_JF:
        if (labels->labels[instr->k].location == 0xffffffff) {
          fprintf(stderr, "Unresolved label: '%s'\n",
                  labels->labels[instr->k].label);
          return 1;
        }
        instr->k = labels->labels[instr->k].location - (offset + 1);
        instr->jt = 0;
        instr->jf = 0;
        continue;
      case (LABEL_JT << 8) | LABEL_JF:
        if (labels->labels[instr->k].location != 0xffffffff) {
          fprintf(stderr, "Duplicate label use: '%s'\n",
                  labels->labels[instr->k].label);
          return 1;
        }
        labels->labels[instr->k].location = offset;
        instr->k = 0; /* fall through */
        instr->jt = 0;
        instr->jf = 0;
        continue;
    }
  }
  return 0;
}

/* Simple lookup table for labels. */
__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label) {
  struct __bpf_label *begin = labels->labels;
  struct __bpf_label *end = begin + labels->count;

  if (labels->count > BPF_LABELS_MAX) {
    return labels->count;
  }
  for (int id = 0; begin < end; ++begin, ++id) {
    if (!strcmp(label, begin->label)) {
      return id;
    }
  }
  if (labels->count == BPF_LABELS_MAX) {
    fprintf(stderr, "Too many labels\n");
    return labels->count++;
  }
  begin->label = label;
  begin->location = 0xffffffff;
  return labels->count++;
}

void seccomp_bpf_print(struct sock_filter *filter, size_t count) {
  struct sock_filter *end = filter + count;
  for (; filter < end; ++filter)
    printf("{ code=%u,jt=%u,jf=%u,k=%u },\n", filter->code, filter->jt,
           filter->jf, filter->k);
}
